Ophthalmology and Optometry are health care professions concerned with the health of the eyes. Ophthalmologists, Optometrists are trained to prescribe and fit lenses to improve vision, and to diagnose and treat various eye diseases. Opticians are trained to fit lenses to improve vision.
Corrective lenses are used to correct refractive errors of the eye by bending the light entering the eye in order to alleviate the effects of conditions such as myopia, hyperopia and astigmatism.
Myopia, which is also known as nearsightedness, is where the light that comes in does not directly focus on the retina but in front of it, causing the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.
Hyperopia, also known as farsightedness or hypermetropia, is a defect of vision caused by an imperfection in the eye such as where the eyeball is too short or the lens cannot become round enough, causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance. When an object moves toward the eye, the eye must increase its optical power to keep the image in focus on the retina. In hyperopia, the power of the cornea and lens is insufficient so the image will appear blurred.
Astigmatism is a defect of vision caused by an irregularity of the cornea or the lens in such as the curvature of the human cornea or lens is different in two main axes—like sitting on a waterball—the vertical axis is steeper than the horizontal one. In human eyes, these axis can differ, hence the degree of the steeper axis has to be detected and documented as from 0 to 179 degrees. These conditions are detected through examination and diagnosis of an eye specialist such as an Ophthalmologist, Optometrist or an Optician.
Photorefraction, invented in the 1970s, is a method to measure the refraction of an eye by analyzing the pupils red reflex using a photograph of the pupil. The core of the principle is analyzing the red reflex of an eye. Up to now, there are only two devices using this principle, both are handheld and expensive since they are infrared based. They cost up to $10,000 dollars or more making it cost prohibitive to use it as a screening device in underdeveloped countries or rural areas.
More on photorefraction is explained in the articles, Measurement of Astigmatism by automated infrared photoretinoscopy, by Florian Gekeler, Frank Schaeffel, Howard C. Howland and John Wattam-Bell, University Eye Hospital, Department of Experimental Ophthalmology, Tuebingen, Germany (FG, FS), Section of Neurobiology and Behaviour, Cornell University, Ihtaca, N.Y. (HCH), and Vision Development Unit, Department of Psychology, University College, London (JW-B). 1997 Optometry and Vision Science Vol 74, No 7, pp 472-482 and Simulation of eccentric photorefraction images, by Ying-Ling Chen, Bo Tan, and J. W. L. Lewis, Center for Laser Applications, The University of Tennessee Space Institute, 411 B. H. Goethert Parkway, Tullahoma, Tenn. 37388-8897, 14 Jul. 2003/Vol. 11, No. 14/OPTICS EXPRESS 1628 which are incorporated by reference.
All photorefractive devices currently available use infrared flashlights. But when using infrared flashlight you have to use special cameras which are able to detect infrared light. Consumer cameras like smartphone-cameras have build-in infrared-blocker to produce natural pictures. Therefore it is up to now not possible to use smartphone cameras as a photorefraction device. Furthermore the flashlight of a smartphone is positioned far away from the axis of the camera, to prevent the unwanted red reflex in portrait photos. Hence you do not get any red-reflex of the eye which is crucial in photorefraction to be analyzed.
There is a need to make the examination and diagnostics for refractive errors of the eye simpler, cheaper and easier to use as well as being portable.
There remains room for improvement in the art.